EV drivetrain inverter with V/HZ optimization

Abstract

An inverter (34) which provides power to an A.C. machine (28) is controlled by a circuit (36) employing PWM control strategy whereby A.C. power is supplied to the machine at a preselectable frequency and preselectable voltage. This is accomplished by the technique of waveform notching in which the shapes of the notches are varied to determine the average energy content of the overall waveform. Through this arrangement, the operational efficiency of the A.C. machine is optimized. The control circuit includes a micro-computer which calculates optimized machine control data signals from various parametric inputs and during steady state load conditions, seeks a best V/HZ ratio to minimize battery current drawn (system losses) from a D.C. power source (32). In the preferred embodiment, the present invention is incorporated within an electric vehicle (10) employing a 144 VDC battery pack and a three-phase induction motor (18).

What is claimed: 
     
       1. An electric vehicle drivetrain comprising: a D. C. power supply;   and A.C. induction motor for driving at least one ground engaging vehicle wheel;   an inverter which receives an input from said power supply through a substantially fixed D.C. bus and provides a PWM power output to said motor at a preselectable frequency and a preselectable voltage; and   a control circuit operative to monitor current delivered through said bus, vehicle operator torque demand and torque delivered by said motor to said wheel, and periodically selectively adjust the ratio of said voltage and frequency only when said torques are substantially equal, as a function of a monitored net change in current effected by a previous ratio variation to minimize input energy through said bus under steady state operating conditions.   
     
     
       2. The drivetrain of claim 1, further comprising means operative to override said ratio variation when the torque demand is not substantially equal to said delivered torque. 
     
     
       3. The drivetrain of claim 2, wherein said override means is incorporated within said control circuit. 
     
     
       4. The drivetrain of claim 1, wherein said ratio variations are in discrete increments. 
     
     
       5. The drivetrain of claim 1, wherein said control circuit monitors the current flowing within said D.C. bus. 
     
     
       6. The drivetrain of claim 1, wherein said A.C. motor is a three-phase induction motor. 
     
     
       7. The drivetrain of claim 1, wherein said control circuit comprises means for generating and momentarily storing said voltage-frequency ratio. 
     
     
       8. The drivetrain of claim 1, wherein said control circuit comprises means operative to compare said demanded torque and machine delivered torque. 
     
     
       9. The drivetrain of claim 1, wherein said voltage/frequency ratio is varied as a function of the net change in current effected by the immediately preceding ratio variation.